X-ray photoelectron diffraction and surface core-level shift study of clean InP (001)

A clean InP(001) surface treated by ion-bombardment and annealing (IBA) has been studied by X-ray photoelectron diffraction (XPD) and synchrotron radiation based photoemission spectroscopy (SRPES). The XPD pattern of In 3d_5/2 (measured at 55° from the surface normal) is compared with a calculated XPD pattern obtained from a single-scattering cluster simulation. Our results indicate that IBA-treated InP(001) exhibits a (2 x 4) surface reconstruction. That is, the two-fold and four-fold directions correspond to the [110] and [110] axes, respectively. For the SRPES study, In 4d core-level spectra (hv = 70 eV) were collected at a variety of photoemission angles. Four spin-orbit doublets were necessary to obtain a high-quality fit to the photoemission spectra. As the detection angle was changed toward the surface parallel, a component having a lower binding energy by 0.70 eV than that of the bulk undergoes a dramatic intensity increase. On the basis of the energy shift and polar angle dependence of this component, we suggest that it arises from surface-layer indium atoms bonded to other indium atoms. The origins of other components are discussed.